I am currently working out on 3 mini-projects and I need some advice and recommendation for the type of sensors to be used.

1. A torch light, but as the user hits it, the light turns becomes brighter. By hitting again(detecting movement/vibration) will turn it back to the lower setting (vice versa).

2. A air refresher, as the user wave it hands back and forth, it activates a spray of scent.

3. A table palm size-speaker, as the user uses his/her hands to cover it, it lowers the volume. When the hand is raised above the speaker, the volume turns louder.

I am still new to Arduino (having a very basic understanding) , would greatly appreciate if anyone could share with me similar projects and tutorial I could learn from and recommend the type of sensors I could experiment with!

To hit something can be detected with a mechanical contact, an accelerometer or a piezo disc (knock sensor).It depends on the device and how you want to hit it. I think that an accelerometer might be the best for this, but perhaps you have to start with something simple.